One of the limiting factors in the operation of large Novell Internetwork Packet Exchange (IPX) internetworks is the amount of bandwidth consumed by the large, periodic Service Advertisement Protocol (SAP) updates. Novell servers periodically send clients information about the services they provide by broadcasting this information onto their connected local-area network (LAN) or wide-area network (WAN) interfaces. Routers are required to propagate SAP updates through an IPX network so that all clients can see the service messages. It is possible to reduce SAP traffic on Novell IPX networks by the following means:

One of the limiting factors in the operation of large Novell Internetwork Packet Exchange (IPX) internetworks is the amount of bandwidth consumed by the large, periodic Service Advertisement Protocol (SAP) updates. Novell servers periodically send clients information about the services they provide by broadcasting this information onto their connected local-area network (LAN) or wide-area network (WAN) interfaces. Routers are required to propagate SAP updates through an IPX network so that all clients can see the service messages. It is possible to reduce SAP traffic on Novell IPX networks by the following means:

Latest revision as of 21:29, 16 October 2012

One of the limiting factors in the operation of large Novell Internetwork Packet Exchange (IPX) internetworks is the amount of bandwidth consumed by the large, periodic Service Advertisement Protocol (SAP) updates. Novell servers periodically send clients information about the services they provide by broadcasting this information onto their connected local-area network (LAN) or wide-area network (WAN) interfaces. Routers are required to propagate SAP updates through an IPX network so that all clients can see the service messages. It is possible to reduce SAP traffic on Novell IPX networks by the following means:

Configuring Cisco routers on Novell IPX networks to run Enhanced IGRP. Although filters provide a means of eliminating the advertisements of specified services, Enhanced IGRP provides incremental SAP updates for a finer granularity of control. Complete SAP updates are sent periodically on each interface only until an IPX Enhanced IGRP neighbor is found. Thereafter, SAP updates are sent only when there are changes to the SAP table. In this way, bandwidth is conserved, and the advertisement of services is reduced without being eliminated.

Incremental SAP updates are automatic on serial interfaces and can be configured on LAN media. Enhanced IGRP also provides partial routing updates and fast convergence for IPX networks. Administrators may choose to run only the partial SAP updates or to run both the reliable SAP protocol and the partial routing update portion of Enhanced IGRP.

Configuring Cisco routers on Novell IPX networks to send incremental SAP updates. With Software Release 10.0, the incremental SAP updates just described can be configured for Cisco routers on Novell IPX networks, without the requirement of running the routing update feature of Enhanced IGRP (only the partial SAP updates are enabled). This feature is supported on all interface types. Again, SAP updates are sent only when changes occur on a network. Only the changes to SAP tables are sent as updates.

To illustrate how to reduce SAP traffic, this case study is organized into two parts:

Figure: Large-scale Novell IPX internetwork

Configuring Access Lists to Filter SAP Updates

Access lists can control which routers send or receive SAP updates and which routers do not send or receive SAP updates. SAP access lists can be defined to filter SAP updates based on the source network address of a SAP entry, the type of SAP entry (file server, print server, and so forth), and the name of the SAP server. A SAP access list is made up of entries in the following format:

where n is between 1000-1099. A network number of -1 indicates any network, and a service type of 0 indicates any service. For example, the following access list accepts print server SAP entries from server PRINTER_1, all file servers, and any other SAP entries from network 123 except those from a server called UNTRUSTED; all other SAP entries are to be ignored:

When checking the entries in a SAP update, each statement in the access list is processed in order, and if there is no match for a SAP entry, it is not accepted. Thus, to block server UNTRUSTED, the deny statement must be placed before the permit for all other devices on network 123.

Two techniques can be used with filtering. Either the SAP entries that are required can be permitted and the rest denied, or the unwanted SAP entries can be denied and the rest permitted. In general, the first method is preferred because it avoids new and unexpected services being propagated throughout the network.

The most common form of SAP filtering is to limit which services are available across a WAN. For example, it does not, in general, make sense for clients in one location to be able to access print servers in another location because printing is a local operation. In this case study, only file servers are permitted to be visible across the WAN.

Central Site

Router A connects to the central site. The following access lists configured on Router A permit everything except print servers from being announced out the serial interface:

IPX Clients

Router C does not require an access list configuration because the remote site does not have any servers. Only Novell servers generate SAP updates.

Configuring Incremental SAP Updates

Incremental SAP updates allow any-to-any connectivity with reduced network SAP overhead. Instead of eliminating the receipt of SAP updates entirely, all necessary IPX services can be broadcast to remote sites only as changes to the SAP tables occur.

Central Site

To configure Enhanced IGRP encapsulated SAP updates to be sent only on a incremental basis, use the following configuration. Although the defined Enhanced IGRP autonomous system number is 999, Enhanced IGRP routing (and routing updates) are not performed because of the rsup-only keyword used with the ipx sap-incrementalcommand. The rsup-only keyword indicates a reliable SAP update.

Remote Sites

This section provides information on the configuration of the routers at the remote sites:

Router B connected to an IPX server and client

Router C connected to two IPX clients

IPX Server and Client

To configure Enhanced IGRP encapsulated SAP updates to be sent only on a incremental basis, use the following configuration for Router B. Although the defined Enhanced IGRP autonomous system number is 999, Enhanced IGRP routing is not performed because of the rsup-only keyword used with the ipx sap-incremental command.

Even though there are no servers, these configuration commands are required to support the incremental SAP updates being advertised from the central site and other remote sites to Router C.

Summary

This case study illustrates two methods of reducing SAP traffic on Novell IPX networks: the use of access lists to eliminate the advertisements of specified services, and the use of the incremental SAP feature to exchange SAP changes as they occur. This technique eliminates periodic SAP updates.